Amphibian conservation fact file

What are amphibians?

Amphibians are cold-blooded (ectothermic) vertebrates and are divided into three groups; frogs and toads, newts and salamanders, and the curiously worm-like caecilians.

Amphibians usually live part of their lives in water and part on land, transforming from aquatic larvae which breathe using gills, to terrestrial adults which breathe oxygen using lungs. However, some amphibians, such as the golden alpine salamander, live permanently on land while others, such as the axolotl, live permanently in water.

First discovered in 2010 in Papua New Guinea, Paedophryne amauensis is not only the world’s smallest amphibian but also the world’s smallest known vertebrate, measuring in at an average 7.7 millimetres long. The world’s biggest amphibian is the Chinese giant salamander, growing up to a staggering 1.8 metres in length.

Why are amphibians under threat?

Amphibians are particularly sensitive to environmental changes due to the permeability of their skin and their complex reproductive systems. Scientists often consider amphibians to be ‘ecological indicators’ as they are among the first species to be affected by changes in environmental conditions, acting as an early warning signal for other species and the wider ecosystem.

Habitat loss, climate change, invasive species, pollution, over-collection and other human influences threaten the world’s amphibian populations. Globally, habitat destruction is one of the most important factors leading to declines in amphibian populations and many other species, largely due to forests being cleared for space and resources for the expanding human population.

However, amphibians are now facing an even greater challenge. In recent years, a lethal infectious disease called chytridiomycosis has emerged as a major contributor to the alarming disappearance of amphibian species worldwide, with the ability to rapidly wipe out entire populations.

What is the chytrid fungus?

Chytridiomycosis is an infectious disease caused by a type of fungus, known as a chytrid, which is found only in water or moist environments. In 1999, scientists described Batrachochytrium dendrobatidis (‘BD’ for short), a new species of chytrid fungus that is able to infect the skin of amphibians.

The chytrid fungus appears to be capable of infecting most of the world’s amphibian species, with many going on to develop the chytridiomycosis disease that is linked to rapid and devastating population declines and species extinctions.

Chytrid fungus has been associated with amphibian die-offs on every amphibian-inhabited continent (all continents apart from Antarctica). Dozens of amphibian species have already vanished as a result of the disease, with 80 percent of amphibians being killed by the fungus in environments where it otherwise thrives.

View a map of the worldwide distribution of the chytrid fungus, Batrachochytrium dendrobatidis.

Effects

Infection with the chytrid fungus occurs inside the cells of the outer skin layers that contain large amounts of a protein called keratin. Keratin is the material that makes the outside of the skin tough and resistant to damage. Chytridiomycosis causes the skin to become thick, a change that is deadly to amphibians because unlike most other animals, amphibians absorb water and salts through their skin. These skin lesions prevent sufficient oxygen from entering the body, effectively suffocating them.

Symptoms

Amphibians that have developed chytridiomycosis can display a variety of symptoms, including reddened or discoloured skin, shedding the skin more than usual, or exhibiting abnormal behaviours such as seizures or nocturnal species becoming active during the day. Many chytridiomycosis symptoms overlap with those of other amphibian diseases, while some species do not exhibit any symptoms at all, and are simply found dead. This makes it difficult for scientists to work out if a species is infected with chytridiomycosis and therefore laboratory testing, such as examining skin samples or swabs under a microscope, is required to diagnose the disease.

Spread of the disease

The most common way that the disease spreads between amphibians is from direct contact of an infected animal with an uninfected animal, for example during mating.
It can also be spread to different locations in water or via moist or wet materials, therefore it is important that biologists working within infected areas take precautions to clean any equipment before moving on to other areas.

Treatment

In captive amphibians, chytridiomycosis can be successfully treated with antifungal medications and by disinfection of contaminated enclosures. Unfortunately, there are currently no methods for treating wild populations.

Why should we conserve amphibians?

In many ecosystems, amphibians make up a key part of the food chain. As predators, amphibians control the number of invertebrates and as prey they are food for many other species of birds and mammals. Therefore, any change in amphibian population numbers will upset the delicate balance of an ecosystem. Amphibians eat pest insects, benefiting agriculture and minimizing the spread of disease, including malaria.

Amphibians have substances in their skin that protect them from some microbes and viruses. Scientists have found ways to use these substances in medicines which could in future be used in treatments for a variety of human infections and diseases, including cancer, Alzheimer’s and the HIV infection that causes AIDS.

Amphibians have also played a vital role in human culture, being regarded as evil in some and cherished as agents of life and good luck in others. Around 220 of the world’s amphibians are used for food, with some being consumed for subsistence and others as ingredients in gourmet food. They are also a source of revenue in the international pet trade.

Amphibian conservation

The dramatic decline in amphibian populations worldwide is considered to be one of most critical threats to global biodiversity, with scientists estimating that half of the world’s 6,000 amphibian species could become extinct within our lifetime. Over 40 percent of all known amphibian species are declining and nearly a third (about 1,895 species) are threatened with extinction.

Methods used to help conserve amphibians include protecting habitats by creating nature reserves and national parks, as well as carrying out public awareness and educational outreach programmes.

Our ability to save the world’s amphibians is not only critical for the survival of the planet’s most threatened vertebrate group, but it will also provide a platform from which we can work together to tackle other major environmental challenges.

Real science: Team WILD

Why do Root and Flora, our Team WILD science superheroes, need to collect uninfected mountain chickens to take to a bio-secure breeding facility?

The Critically Endangered mountain chicken is one of the world’s most threatened species of frog. Also one of the largest frogs in the world, growing up to remarkable lengths of 21 centimetres, this curious species is the top endemic predator on its island home of Montserrat and Dominica.

Mountain chicken populations have undergone catastrophic declines, estimated at around 80 percent over the past 10 years. The mountain chicken has fallen victim to habitat loss, invasive species, hunting by humans, volcanic activity and the arrival of the deadly chytrid fungus. The species’ range is now restricted on Dominica to around 25 km² and to about 20 km² on Montserrat.

The chytrid fungus was first identified in Dominica in 2002. The disease spread rapidly, resulting in an 80 percent population decline in mountain chickens within the first two years. The first confirmed cases on Montserrat were discovered in February 2009, with similar mortality rates to those witnessed on Dominica with 80-90 percent of individuals dying. Although the original source of the fungus remains unknown, it is thought that it was brought onto the islands via frogs stowed away on ships.

Working together, the organisations and their team of dedicated scientists lead conservation efforts for each island on the ground, as well as managing a captive breeding and reintroduction programme. In addition, the mountain chicken recovery programme carries out critical research into the ecology and management of the chytrid fungus, contributing to the global conservation of the world’s amphibian species.

Following the identification of the chytrid fungus on Montserrat in 2009, a rescue mission collected 50 frogs from the wild and entered them into a bio-secure captive breeding programme, transporting individuals to partner institutions such as Durrell Wildlife Conservation Trust. Due to the work of dedicated herpetologists (amphibian specialists), the species has successfully bred in captivity, with these captive populations forming the basis of a safety-net population should the species become extinct in the wild.

In January 2012, a healthy population of 33 mountain chickens was released back into the forests of Montserrat. The frogs were released with electronic tags to help scientists’ track their movements and healthy individuals are still being found, enabling scientists to collect location data and skins swabs. Although some of the released frogs have been found to be infected with the chytrid fungus, this could help the scientists to better understand the disease that is decimating amphibian populations worldwide.

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